Extreme Drought to Flood in Georgia: Weather Whiplash Strikes Again

The remarkable storm that brought record-breaking May snows and cold to the Midwest last week continues to spin over the Southeast U.S. The storm is unleashing flooding rains, bringing a case of "Weather Whiplash" to Georgia: flooding where extreme drought had existed just a few months ago. The storm formed when a loop in the jet stream of extreme amplitude got cut off from the main flow of the jet over the weekend, forming a "cutoff low" that is now slowly spinning down as it drifts east over the Southeast U.S. On Sunday, the storm dumped 3.4" of rain on Atlanta, Georgia--that city's sixth heaviest May calendar day rain storm since record keeping began in 1878. Remarkably, the rains were also able to bring rivers in Central Georgia above flood stage. This portion of the country was in "exceptional drought"--the worst category of drought--at the beginning of 2013.

Figure 1. The record May snowstorm that hit the Midwest U.S. on May 1 - 3, 2013, got cut off from the jet stream and was seen spinning over the Southeast U.S. on Sunday, May 5, in this image from NASA's MODIS instrument. The 3.4" of rain that fell on Atlanta, Georgia on May 5 was that city's sixth heaviest May calendar day rainfall since record keeping began in 1878.

Weather WhiplashWeather Whiplash--a term originally coined by science writer Andrew Freedman of climatecentral.org to describe extreme shifts between cold and hot weather--is also a excellent phrase we can use to describe some of the rapid transitions between extreme drought and floods seen in recent years. I brought up a remarkable example in mid-April, when a 200-mile stretch of the Mississippi River north of St. Louis reached damaging major flood levels less than four months after near-record low water levels restricted barge traffic, forcing the Army Corp to blast out rocks from the river bottom to enable navigation. As the climate warms, the new normal in coming decades is going to be more and more extreme "Weather Whiplash" drought-flood cycles like we have seen in the Midwest and in Georgia this year. A warmer atmosphere is capable of bringing heavier downpours, since warmer air can hold more water vapor. But you still need a low pressure system to come along and wring that moisture out of the air to get rain. When natural fluctuations in jet stream patterns take storms away from a region, creating a drought, the extra water vapor in the air won't do you any good. There will be no mechanism to lift the moisture, condense it, and generate drought-busting rains. The drought that ensues will be more intense, since temperatures will be hotter and the soil will dry out more.

Figure 2. Weather Whiplash in Georgia, 2013: the center of the state was in exceptional drought as the beginning of the year, but heavy rains in February, March, and April busted the drought. Heavy May rains have now brought flooding. Image credit: U.S. Drought Monitor.

Weather Whiplash in the Southeast U.S. more likely due to an intensification of the Bermuda HighThis year's "Weather Whiplash" in Georgia is the second time in the past decade the state has gone from exceptional drought to flood. In September 2007, Atlanta, Georgia was in the midst of a 1-in-100 year drought, and was just weeks away from running out of water. Yet just two years later, the drought had been busted, and a phenomenal 1-in-500 year flood ripped through the city, killing ten and causing $500 million in damage. According to a 2011 study by a Duke University-led team of climate scientists, "Changes to the North Atlantic Subtropical High and Its Role in the Intensification of Summer Rainfall Variability in the Southeastern United States", the frequency of abnormally wet or dry summer weather in the southeastern United States has more than doubled in recent decades, due to an intensification of the Bermuda High. The scientists found that the Bermuda High, which is centered several hundred miles to the east of the Southeast U.S., has grown more intense during summer and has expanded westwards over the past 30 years. Since high pressure systems are areas of sinking air that discourage precipitation, this has made abnormally dry summers more common over the Southeast U.S. However, in summers when the Bermuda High happens to shift to the east, so that high pressure is not over the Southeast U.S., the stronger winds blowing clockwise around the Bermuda High bring an increased flow of very moist subtropical air from the south to the Southeast U.S., increasing the incidence of abnormally wet summers. Thus, the intensification of the Bermuda High has made extreme droughts and extreme floods more likely over the Southeast U.S. Using climate models, the scientists determined that human-caused global warming was likely the main cause of the significant intensification in the Bermuda High. Thus "Weather Whiplash" between drought and flood will probably become increasingly common in the coming decades over the Southeast U.S.

Figure 3. Observed June-July-August departure of precipitation from average over the SE United States for a 60-yr period (mm day−1). Horizontal dashed lines represent 1 standard deviation of the summer rainfall. Note that summer precipitation extremes exceeding one standard deviation have more than doubled during the most recent 30-year period compared to the previous 30-year period. Image credit: Li et al., 2011, Journal of Climate.

We've had something to watch in the Western Caribbean in late May/early June the past 3 years. I have been watching with interest the long range GFS which has been hinting at tropical stirrings in this area of the world around that time. It will be something to keep an eye on for sure.

The 12-15 day GFS has had "something" in the western Caribbean literally almost every run for the last 3 weeks. It is next to useless in the early season because it has a bias of allowing the monsoonal circulation to invade the Caribbean.

If it shows a robust cyclone that leaves the Caribbean Sea, then that might be a clue to the future, but "rumblings in the deep" at the end of the GFS run almost never mean anything this time of year.

All of that said, ever since the twin Indian TCs were forecasted back in late April, I've been saying it could set up the EPAC / Caribbean in late May or early June, so I think we will have to watch that region soon enough.

That would be incorrect. Global warming is one facet--or symptom, if you will--of climate change. The two terms are not interchangeable by scientists, nor have they ever been; while some may be confused about the terminology, climatologists certainly aren't.

I'm very pleased to see that the Guardian is filling in where other outlets, swayed by perhaps by a lazy desire to provide "balance" where none truly exists, have become lax in their journalistic duties. Kudos to them for providing an invaluable service...

So, the Earth's average temperature has increased about 1 degree Fahrenheit during the 20th century. What's the big deal?

One degree may sound like a small amount, but it's an unusual event in our planet's recent history. Earth's climate record, preserved in tree rings, ice cores, and coral reefs, shows that the global average temperature is stable over long periods of time. Furthermore, small changes in temperature correspond to enormous changes in the environment.

For example, at the end of the last ice age, when the Northeast United States was covered by more than 3,000 feet of ice, average temperatures were only 5 to 9 degrees cooler than today.

The hurricane return period for the Tampa Bay area and northeast Florida/South Georgia should be in the 25 to 50 year color coding.

That just doesn't seem right, there is absolutely no way the hurricane return period here around Tampa Bay is shorter than western Louisiana and is supposedly the same as the western Florida panhandle/Alabama/Miss coastline...

They are not speaking of a direct strike, but of estimated times a hurricane coming within 50 nautical miles of a given area based upon historical estimates.

* URBAN AND SMALL STREAM FLOOD ADVISORY FOR HEAVY RAINFALL AND MINOR FLOODING IN... DURHAM COUNTY IN CENTRAL NORTH CAROLINA... WAKE COUNTY IN CENTRAL NORTH CAROLINA...

* UNTIL 330 PM EDT

* AT 206 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED THUNDERSTORMS WITH HEAVY RAINFALL OVER WAKE AND DURHAM COUNTIES. DOPPLER RADAR ESTIMATED A HALF INCH TO AN INCH OF RAIN HAS FALLEN SINCE 100 PM. ADDITIONAL RAINFALL AMOUNTS OF UP TO AN INCH WILL BE POSSIBLE THROUGH 300 PM.

* RUNOFF FROM THIS HEAVY RAINFALL WILL CAUSE MINOR FLOODING TO OCCUR...ESPECIALLY ALONG SMALL STREAMS...IN LOW LYING AREAS...AND AREAS OF POOR DRAINAGE. SOME LOCATIONS THAT WILL EXPERIENCE MINOR FLOODING INCLUDE...CARY...DURHAM...RALEIGH...FUQUAY-VARINA. .. GARNER...RDU INTERNATIONAL...ROUGEMONT AND WAKE FOREST.

We've had something to watch in the Western Caribbean in late May/early June the past 3 years. I have been watching with interest the long range GFS which has been hinting at tropical stirrings in this area of the world around that time. It will be something to keep an eye on for sure.

Quoting StormTrackerScott:MJO increases across the Caribbean come late May.

We've had something to watch in the Western Caribbean in late May/early June the past 3 years. I have been watching with interest the long range GFS which has been hinting at tropical stirrings in this area of the world around that time. It will be something to keep an eye on for sure.

this also contributes to why the Western Caribbean generally gets the most storms than anywhere else in the Atlantic Basin Western Caribbean this mainly includes Cayman Islands Cuba Honduras and Jamaica

also area like S Florida Yucatan and Bahamas thought these are more like secondary targets for most storms

In May it is common for an area of low pressure to get drawn north off Panama or South America into the SW Caribbean. That is why the western Caribbean can be active at times in Late May.

this also contributes to why the Western Caribbean generally gets the most storms than anywhere else in the Atlantic Basin Western Caribbean this mainly includes Cayman Islands Cuba Honduras and Jamaica

At first it was blaming human caused global warming because the globe was warming. Now we're blaming human caused global warming on extreme cold, warmth, drought, floods etc.... So I guess we can blame human caused global warming on just about every weather event that happens. Temps are below normal here in Florida today. I blame global warming.